The present invention relates generally to mounting methods and more particularly to a method for mounting power devices that are heat sinked to a chassis or housing.
Those skilled in manufacturing techniques can appreciate the significant problems encountered when trying to align a power device to a heat sink in a housing. Several critical factors must be controlled to ensure proper alignment of the power device to the mounting hole or position on the heat sink. The paramount alignment factors include the height of the device above the printed circuit (PC) board, the alignment of the PC board within the housing, and the registration of the mounting location on the heat sink. While each of the individual parameters may be within a specified tolerance, when assembled, the tolerance buildup results in non-alignment of the power device and the mounting location. Clearly, the alignment problem is multiplied if multiple power devices require mounting in a common housing.
The alignment problem cannot be corrected by placing more stringent specifications on the individual parts since this will generally increase the cost of the individual parts, and thus the entire assembly, such that their use becomes cost prohibitive. Alternately, some process control engineers have elected to mount the power device as an individual component at the final assembly stage of the manufacturing process. Generally, this technique succeeds in removing the height of the part above the PC board parameter, however, does not improve the alignment of the PC board in the housing or the registration of the mounting location on the heat sink.
Typically, the PC board would be mounted into the housing and the power device manually arranged until alignment was satisfactory after which the device would be affixed to the heat sink. In addition to being laborious, this technique places physical stresses on the terminal leads of the power device as it is "force fitted" into alignment. Those skilled in the art will appreciate that physical stresses on terminal leads may affect the internal bonding of a device and hence shorten the device lifetime. Thus, a need exists to find a method for mounting power devices to a heat sink that eliminates the aforedescribed tolerance and stress problems encountered when trying to mount a power device to a heat sink.